[PDF] Mole & Molar Mass - Montgomery College

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Mole & Molar Mass

Mole (mol): the amount of material counting 6.02214 × 10 23
particles The value of the mole is equal to the number of atoms in exactly 12 grams of pure carbon-12. C-12 = 1 mol C-12 atoms = 6.022 × 10 23
atoms The number of particles in 1 mole is called Avogadro's Number (6.0221421 x 10 23
).

6.022 ×10

23
atoms 1 mol or 1 mol

6.022 ×10

23
atoms

Converting between Number of

Moles and Number of Atoms

Calculate the number of atoms in 2.45

mol of copper. A silver ring contains 1.1 x 10 22
silver atoms. How many moles of silver are in the ring?

2.45 mol Cu ×

6.022 ×10

23
atoms

1 mol

= 1.48 × 10 24
atoms Cu 1.1 ×10 22
atoms Ag × 1 mol

6.022 ×10

23
atoms = 1.8 × 10-2 mol Ag Molar Mass: the mass of 1 mol of atoms of an element An element's molar mass in g/mol is numerically equal to the element's atomic mass in amu.

1 mol C

C or C

1mol C

Converting between Mass and Number of MolesConverting between Mass and Number of Atoms

Calculate the moles of carbon in of

pencil lead. How many aluminum atoms are in a can weighing 16.2 g? C ×

1 mol C

C = 2.21 × 10 -3 mol C Al ×

1 mol Al

26.98 g Al

×

6.022 ×10

23
atoms

1 mol

= 3.62 × 10 23
atoms AlAtoms mol Cu g Al mol Al atoms Al mol Ag Atoms Ag mol C g C

Practice Problems

1. How many atoms are there in each of following?

(a) 3.75 moles of silver (b) 2.36 moles of xenon (c) 158 kg of phosphorus

2. What is the amount, in moles, of each of the following?

(a) of potassium (b) of Ar (c) 2.16 x 10 24
atoms of lead

3. What is the mass of each of the following?

(a) 1.9 x 10 24
atoms of Pb (in g) (b) 4.87 x 10 25
atoms of Zn (in kg) (c) 2.33 x 10 20 atoms of oxygen (in ng)

4. How many molecules are in 2.50 moles of CO

2 ?

5. Calculate the mass , in grams, of 0.433 mol of calcium nitrate.

Hint: Formula Weight of Ca(NO

3 ) 2 = (AW of Ca) + 2(AW of N) + 6 (AW of O)

6. Calculate the number of H atoms in 0.350 mol of C

6 H 12 O 6

References:

Tro, Chemistry: A Molecular Approach 2

nd ed., Pearson Brown/LeMay/Bursten, Chemistry: The Central Science, 12 th ed., Pearson

Answers

1. (a) 2.26 × 10

24
silver atoms; (b) 1.42 × 10 24
xenon atoms (c) 3.07 × 10 27
phosphorus atoms

2. (a) 11.5 moles; (b) 0.295 moles Ar; (c) 3.59 moles

3. (a) ) 6.5 × 10

2 g; (b) 5.29 kg; (c) 6.19 × 10 6 ng

4. 1.51 x 10

24
atoms; 5. 71 Ca(NO 3 ) 2 6. 2.53 x 10 24
H atoms Gram Moles Formulaunits (atoms, molecules, ions) molar mass

Avogadro's

number